Storage tanks are widely used for storing a variety of liquids. Some of these liquids are hazardous and can be corrosive and/or flammable. In particular, underground storage tanks are used extensively for the storage of liquid gasoline at retail gasoline stations. Typical underground storage tanks are constructed with structural accessories such as a manway, its lid, and access lines for filling, dispensing, and venting. The accessories described are examples of structures through which liquids and vapors flow and all of which are normally located at the top of the tank.
The access line which has proved most troublesome to adequately ensure against spillage and leakage has been the line for periodically filling the storage tank. This line extends from ground surface to the underground storage tank. Spillage at ground surface level can occur when the line is accessed by a transport tank truck operator for filling of the storage tank. Extreme care must be taken so that minor drippings do not occur since even minor drippings from repeated fillings over a course of years can ultimately become excessive. Drip sumps around the ground surface level of the fill line have helped.
Another problem experienced by the fill lines is that if made of steel, as is conventional, they tend to corrode from contact with surrounding soil. A drip sump which extended from ground surface to the storage tank would appear to solve the problems in that it would catch accidental drippings from the filling operation as well as protect the fill line from contact with the soil. However, a deep drip sump itself creates problem in that debris which enters is difficult to remove because of the depth.
A large secondary containment area to encompasses all the access lines has been suggested. This would allow for better access means to enter the area and reach the various fittings, remove debris, etc. However, any drippings which reach any such relatively large containment area, whether directly or indirectly, create a potentially dangerous situation. The drippings can vaporize and with the right vapor-oxygen ratio can explode if an ignition source is present such as from electrical equipment often contained at or near the storage tank's access lines or hot exhaust gas from a vehicle. As can be appreciated, there are several requirements that must be considered in the designing of a containment system for access lines to an underground tank.
The service life of a storage tank system will vary, but eventually the tank and its access lines will leak. Leaks from the tank system often happen within a few years after the new tank and lines are installed, due to improper installation or flaws in the manufacturing of the tanks and lines. Leakage problems are particularly troublesome in that gasoline storage tanks are usually buried underground. Any leaks which develop are normally very slow initially and are very difficult to detect. Leaks from subterranean tanks or their accessories can result in a significant danger to the environment and health of nearby residents. Federal as well as local regulations govern the design and maintenance of such storage tanks.
Heightened public awareness of the danger posed by underground storage tanks has led to additional governmental regulations. Recent proposed regulations will require most storage tanks to have secondary containment means and possibly a fail safe leak detection design feature to guard against accidental soil and water contamination. Secondary containment is accomplished by a jacket completely encasing the tank and structural accessories. The tank and related accessories are referred to as the primary containment system. Any jacket or wall encasing the primary system is often referred to as a secondary containment system. While seemingly simple in design, total containment with full consideration for all aspects of the system has been difficult.
There now has been discovered a system for enclosing the fill line and, optionally, other structural accessories of a liquid underground storage tank which solves problems associated with many known systems. Additionally, the storage tank itself can have a secondary containment feature. The present invention solves the problems inherent with existing tank systems. It is useful with new tank systems and as well as a retrofit to buried tank systems.